The present invention relates generally to controlled motion systems and more specifically, the present invention relates to controlled motion systems having more than one linear motor sections and means of joining the linear motor sections together using a magnetic flux bridge such that the likelihood of interruption or a change in the level of magnetic flux along and between the linear drive sections is reduced.
The application of controlled motion systems to a wide variety of processes (e.g. for packaging, transporting objects, assembly automation, and processes involving use of machine tools, etc.) provides the advantage of increasing both the speed and flexibility of the process. Controlled motion systems comprise linear motors, such as linear motors, that employ a moving magnetic field to directly motor a moving element, sometimes known as a carriage, pallet, tray, or mover (referred to here collectively as a “mover”). Such linear motors reduce or eliminate the need for gear heads, shafts, keys, sprockets, chains and belts often used with traditional rotary motors. This reduction of mechanical complexity provides both reduced cost and increased speed capability by virtue of reducing inertia, compliance, damping, friction and wear normally associated with more conventional motor systems. Further, controlled motion systems also provide greater flexibility than rotary motor systems by allowing each individual mover to be independently controlled along its entire path.
Controlled motion systems typically comprise interconnected track sections, each section has a plurality of individually controlled coils that provide independent control of one or more movers that travel along the track. Such systems include a positioning system that often employs a plurality of linear encoders spaced at fixed positions along the track and linear encoder strips mounted on each mover to sense their position. Such linear encoders are typically “incremental absolute” position encoders that are coupled to a controller or counter, and that operate by sensing and counting incremental pulses (or that digitize sine/cosine signals to create these pulses) to count up or down after a mover has traveled past a reference point. Such incremental encoders, however, can provide an absolute position signal only after performing a homing and commutation alignment procedure for each mover at power up. This requires moving each mover a certain distance along the track to find the zero reference position and the magnetic pole positions.
The prior art is filled with similar such controlled motion systems utilizing linear motors. However, such systems suffer from a particular deficiency. Specifically, tracks are generally assembled by combining individual track sections, wherein each section is adhered or connected to an adjacent section along their contact surfaces, such as by use of an epoxy or other such material, and then covered or encased in stainless steel or similar material. During actual use of the system, a mover travels along the track from section to section through employment of a magnetic field created by the individually controlled coils positioned along each section of the track. Often, the region between where the mover leaves one section of the track and reaches the next section, there is typically a disturbance or weakening in the magnetic field that results in a relatively large increase in resistance or cogging as compared to the magnetic field in the middle of a section. This disruption or weakening in the magnetic field is a result of an air gap along the contact surfaces of the assembled track sections generally caused by non-precise milling of the adjacent track sections so exposed cores do not magnetically touch, or by the epoxy or other non-magnetic covering (i.e., stainless steel) creating a substantially non-magnetic gap between the individual track sections. This disruption or weakening in the magnetic field between adjacent track sections is problematic in that it often leads to lost performance, noise, false readings, or crashes along the track. Further, when a mover experiences a disruption or weakening in the magnetic field during operation of the motion control system, the counting process by the controller or counter is often lost or the pulse counting disrupted. Such disruption or weakening requires the movers to be driven back to a reference point of home position to initialize or reset the counting process. This initialization or resetting of the counting process results in significant loss of production time and often lost product. Further, depending on the location, the disruption or weakening can result in stoppage of the entire control motion system often resulting in the need to reset or restart other processes.
Accordingly, what is needed is a controlled motion system comprising one or more linear motors positioned along a track formed from two or more sections such that the likelihood of interruption or the level of disturbance or weakening in the magnetic field along and between adjacent linear motor sections is reduced or minimized.